This invention relates to a steerable pipe jacking head for laying small diameter pipes such as gas, water, and the like conduits, precisely in position underground. In particular, the invention relates to an apparatus and method for steering a pipe jacking head in two degrees of freedom, i.e. vertical and horizontal directions.
Heretofore, apparatus have been provided for laying pipes in the ground such as drainage, gas, water pipes, and the like, of relatively small diameter. Typically, pipe casings are pushed through the ground by the use of a hydraulic jack which advances a link of pipe casing underground and then is retracted. A new link of pipe casing is then threaded onto the advanced pipe casing and is itself advanced. The procedure is repeated until a desired length of pipe casing has been pushed underground. The problem arises of steering the string of pipe casings as they are pushed through the ground. Often, it is necessary to go underneath a conduit, creek bed, and the like, so that the desired path for the pipe casing is usually not straight. In any event, it is difficult to maintain a straight advance of the laid in pipe casings. It has been proposed to provide a detector pipe extending along the axis of the laid in pipes which may be detected so as to measure a vertical position of the forward end of the laid in pipe casings. Typically, a transmitter is located at the forward end of pipe casings and a receiver is utilized above ground to locate the forward end of the pipe casings. However, this is not entirely reliable since there are numerous factors underground which can interfere with the transmission and accuracy of the signal. Even if the vertical position of the front end of the pipe is known, it is often difficult to steer the string of laid in pipe casings when deviations occur in the detected vertical position. While the problems of detecting and steering in regards to vertical positions are difficult, the measuring and steering in a horizontal plane are even more difficult. The directional control of small diameter pipes which are pushed through the ground requires not only skilled operators, but reliable means of measuring the position and then steering the forward end of the pipe casings. Suitable measuring and steering devices have not been provided by the prior art. U.S. Pat. No. 4,026,371 discloses a pilot head for laying small diameter pipes which comprises an expandable and contractible pilot jack disposed within a pilot casing, a pivoting cylinder adapted for pivoting the pilot jack in a selected direction in a plane normal to the central axis of the pilot head, and an electromagnetic valve for operating the cylinder. A clinometer is used for detecting the vertical position angle and direction of the pilot head. However, the mechanism for pivoting the pilot jack involves ball joints which easily become worn, particularly when considering the pressure exerted on such a pipe jack due to the compression of the soil as the pipe head is advanced by a hydraulic or other jack through the ground. While the patent discloses both measuring the vertical position with a clinometer and/or transit, there is no means provided for measuring the horizontal position or for steering the pipe head according to a desired heading. Even if a cased bore is formed with pipe casings along a desired vertical direction, many times the cased bore will be off several feet to the left or right. When this occurs, it is often necessary to relay the pipe casings to form another cased bore, hopefully more accurately in line. This involves considerable additional expense and effort. It is not guaranteed that the second cased bore will be any more accurate in its horizontal position than the first.
Accordingly, the problem of measuring the vertical and horizontal positions of a pipe casing which is jacked or pushed through the ground, and of steering a forward end of the pipe casing in both a horizontal and vertical direction, is a problem to which considerable attention need be given.
Accordingly, an object of the invention is to provide an apparatus and method for guiding and steering a pipe jacking head in two degrees of freedom.
Another object of the invention is to provide a simple, yet reliable, means for guiding and measuring a steerable pipe jacking head in two degrees of freedom, that is both the horizontal and vertical directions.
Another object of the invention is to provide an apparatus and method which is simple in construction and yet is effective for steering a pipe jacking head in both a horizontal and vertical direction as pipe casing is pushed underground from a pit station.
Another object of the invention is to provide an effective steering device for a steerable pipe jacking head which may be extended to steer the pipe jacking head and change direction and then retract it so that the pipe jacking head may be pushed in that direction until a further direction change is needed.
Another object of the invention is to provide a simple and reliable guidance system for measuring the horizontal and vertical positions of a steerable pipe jacking head having such an effective steering device.